January 18, 2010

Feet May Have Played Role In Hand Evolution

A group of scientists may have solved the mystery of how human hands became nimble enough to make and manipulate stone tools, according to BBC News.

The team wrote in the journal Evolution that changes in the shape of our feet effected the changes in our hands and fingers.

According to their report, this shows that the capacity to stand and walk on two feet is intrinsically linked to the emergence of stone tool technology.

The researchers used a mathematical model to simulate the changes.

Other scientists have questioned their approach.

Campbell Rolian from the University of Calgary in Canada led the study and said, "This goes back to Darwin's The Descent of Man."

"[Charles Darwin] was among the first to consider the relationship between stone tool technology and bipedalism. His idea was that they were separate events and they happened sequentially - that bipedalism freed the hand to evolve for other purposes. What we showed was that the changes in the hand and foot are similar developments... and changes in one would have side-effects manifesting in the other."

Rolian and his colleagues took measurements from the hands and feet of humans and of chimpanzees to study this.

Their goal was to see how the hands and feet of our more chimp-link ancestors would have evolved.

The group took measurements that showed a strong correlation between similar parts of the hand and foot. "So, if you have a long big toe, you tend to have a long thumb," Dr Rolian explained.

"One reason fingers and toes may be so strongly correlated is that they share a similar genetic and developmental 'blueprint', and small changes to this blueprint can affect the hand and foot in parallel," he said.

The researchers were able to take this data and create their mathematical simulation of evolutionary change.

"We used the mathematical model to simulate the evolutionary pressures on the hands and feet," Dr Rolian explained.

The model adjusted the shape of the hands or the feet, recreating each of the small evolutionary changes to see what effect they had.

The team found that changes in the feet caused parallel changes in the hands, especially in the relative proportions of the fingers and toes.

Rolian said that these parallel changes, or side effects, might have been an important evolutionary stem that allowed human ancestors, including Neanderthals, to develop the dexterity for stone tool technology.

Professor of anatomy at the U.K.'s Liverpool University, Robin Crompton, told BBC the study was very interesting but also raised some questions.

"I am not personally convinced that the foot and hand of chimpanzees are a good model [of human ancestors' hands and feet] - the foot of the lowland gorilla may be more interesting in this respect," he told BBC News.

He said there was a lot more to the functional shape and biomechanics of the human foot than just its proportions.

Paul O'Higgins, professor of anatomy at the Hull York Medical School, U.K., told BBC, "The results are quite exciting and will doubtlessly spur further testing and additional work."